vCenter Storage Status “unknown”

I’ve seen a few cases where storage devices (specifically iSCSI or FCP datastores) return a gray “unknown” for a status:

In all the cases I have seen the culprit was disabling the default “Datastore usage on disk” alarm at the vCenter server object. I usually see this disabled when custom alarms are created for specific datastore objects and at least one datastore object will exceed the 75/90 warning/alarm for the default rule, or when you don’t want to be alerted if a specific store does: In this example I don’t care of the NFS datastore exceeds 75 or 90% because it only holds ISOs, but I do want the others to alarm. I’ve set an alarm for each storage folder to ensure I get the alarm I need.

Then instead of disabling the default alarm, set the warning to 99 and the alarm to 100%

Now I don’t see the alarm if the NFS datastore hits 75, but I do for the others, and the “status” column still works.